A current copy of an old music recording may not run at the correct speed during playback. This problem is due to incorrect speed settings of playback and/or recording machines used when the recording was originally made or during subsequent copying. The desired solution is to playback the music at a pitch of the original sound of the recording without an error of the pitch.
A current way to implement the solution is to listen to the opening music of the recording and (change the playback speed to) match it with an existing opening music recording without a pitch error. This approach requires a listener with a good ear. Also required is another recording with a piece of the same music. If the second recording also has an error, the results will not be accurate. The results will be subjective. A second way to playback music at the pitch of the original recording is to change the length of the original recording. For example, if it is a half an hour program, adjust speed of the recording so that it plays for about 29 minutes. The drawback here is that it is useable only for recordings where the original playback time is exactly known. If the recording was originally made on a machine with an incorrect speed (and playback time of that recording was recorded) it will not be possible to Find the correct pitch of the original music using this method.
The general task of accurately reproducing sounds (audio waveforms) has been the subject of much research development. U.S. Pat. No. 6,721,771 describes an audio waveform reproduction apparatus. In this approach, the audio waveform reproduction apparatus includes a storage means for storing waveform data of the audio waveform, an input means for inputting reproduction tempo information, a first information production means for producing first information (TP) that is a time function based on the reproduction tempo information, a second information production means for producing second information (PP) that is a time function based on time axis compression/expansion information (TR), a compression/expansion information production means for comparing the first information and the second information and calculating the time axis compression/expansion information (TR) towards matching the temporal change of the second information with the temporal change of the first information, and a time axis compression/expansion processing means for performing time axis compression/expansion processing based on the time axis compression/expansion information (TR) to produce a reproduction audio waveform, wherein the first information (TP) and the second information (PP) represent positions on a common axis.
U.S. Pat. No. 6,490,553, describes a method for reproducing musical sounds is disclosed. Musical sounds and voices are stored and reproduced with user-definable timing and pitch, with the timing and pitch being independently controllable in real time. Musical sounds are stored in waveform memory, and pitch and timing information may be received in real time. The stored musical sounds and voices are then reproduced in accordance with the received pitch and timing information. The reproduction of stored musical sounds can also be stopped and resumed at user-definable marks.
U.S. Pat. No. 4,406,001, describes a time compression/expansion audio reproduction system of the type that provides pitch correction by repetitive variable time delay achieves improved performance by separating the reproduced signal from a recording into components, which are separately delayed. For studio quality reproduction the signal is separated into contiguous frequency bands, which are, each delayed synchronously and filtering each band signal after delay to eliminate high frequency components eliminates the processing noise in each band.
Although there have been numerous efforts to accurately reproduce sound/audio waveforms, with regard to the playback of musical recordings, there still remains a need for a method to adjust the pitch of the recording such that the pitch of a note at any point in the recording is similar in tone to the original pitch for that note.